TTL and opto-coupler signal

Discussion in 'Embedded Systems and Microcontrollers' started by Tiak, Jan 24, 2011.

  1. Tiak

    Thread Starter New Member

    Jan 24, 2011
    5
    0
    Hi

    I'm working on at serial gateway, and i'm not 100% sure how get my device connected right to my Arduino.
    And now i really need some help from a super electrical guy.

    The normal way connecting to the heat meter is that i have a serial cable from the manufacturer
    and the communication from the PC to the meter is RS232. se schematic

    [​IMG]

    But i don't wont to use this cable also i don't wont to build a RS232 to TTL
    converter, be curs my arduino only have TTL available 5v, so i talk with the manufacturer and he told me that it shut work with this schematic

    [​IMG]
    http://pdfcast.org/pdf/1716003-sharp-pc357

    But it don't work and i only have a small knowledge about Electronics so i hope someone can help me, i think that there is a problem with getting the opto coupler to work.


    Device "heat meter" i need to send data from Arduino to heat energy meter and receive data."
    1200/8/2/N

    Hope someone can help
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    This is how I often do an isolated RS232 connection to/from a microcontroller. It does, however, require the use of a small DC-DC converter to get the isolated ±12V supplies.
     
  3. Tiak

    Thread Starter New Member

    Jan 24, 2011
    5
    0
    Okay so the schematic i have of my arduino and the interface with the resistor will not work in my case if i understand you right?.

    The thing is that the microcontroller of the heat meter "as i know it" also run TTL and the only thing the interface Bord is doing is protecting the microcontroller, so is it not possible to get the opto coupler "running" without DC to DC converter scene i'm not using RS232.

    Just to bee 100% clear the internal side of the schematic i going to the heat meters controller, the supply voltage is i think not more than 3.6 v on pin J2-3 and + on J2-6, but the internal side i don't won't to play around, is't only the Arduino side of the interface bord im connecting.
     
    Last edited: Jan 24, 2011
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Have you looked at the MAX232, or one similar to it?

    While searching for stuff, I found This A USB Arduino from FTDI, which is pretty cool.
     
  5. Tiak

    Thread Starter New Member

    Jan 24, 2011
    5
    0
    No i have not used the MAX232, be curs i don't need to convert the TTL signal from the arduino it's already a TTL signal both Arduino side and the Interface side on the heat meter..

    The pin i use on the Arduino is

    Pin 0 RX
    Pin 1 TX
    5V to the pull up resistor
    GND

    The Arduino i use is the Arduino UNO
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Is there a reason the TTL Levels must be isolated? Different power sources/levels?
     
  7. Tiak

    Thread Starter New Member

    Jan 24, 2011
    5
    0
    I'm not sure but i think to protect the equipment but also the TTL voltage on the heat meter is 3.3V, and on the arduino it's 5V.

    I think the best way is to keep the small interface with the 2 isolator, but then the question is how to get the 2 isolator to work together whit the TTL levels from the arduino, and thats my problem

    Jesper
     
    Last edited: Jan 25, 2011
  8. Tiak

    Thread Starter New Member

    Jan 24, 2011
    5
    0
    Does some body think that a pull op resistor on the TTL TX output from the Arduino, will help drive the OPTO cobbler, and if so have someone an ide off the size of the resistor?
     
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